The present invention relates generally to an internal combustion engine cooled or heated by circulating a heat carrier such as cooling water etc, and more particularly to an internal combustion engine including a heat accumulation system for accumulating the heat held by the heat carrier.
In the case of executing a cold start-up of the internal combustion engine, a temperature of a wall surface of each of an intake port and a combustion chamber is low, and therefore a temperature of suction air is easy to decrease corresponding thereto. When the temperature of the suction air of the internal combustion engine is low, a fuel is hard to vaporize and is easy to adhere to the wall surface of the combustion chamber etc, and hence there is a necessity of increasing a quantity of fuel injection in a way that takes a wall surface adhered fuel quantity into account.
When the temperature of the suction air of the internal combustion engine is low, a temperature of an air/fuel mixture at a compression stroke is lowered, so that an ignitability of the fuel is easy to decline and a comparatively large quantity of fuel is easily discharged from the internal combustion engine as the fuel remains unburned.
Further, if the internal combustion engine is classified as a water cooled internal combustion engine, a temperature of the cooling water is lowered when performing the cold start-up of the internal combustion engine. It is therefore impossible to exchange the heat between the cooling water and the air for heating an interior of a car room and is difficult for an car room interior heating system to exhibit a sufficient performance.
Thus, when the internal combustion engine is in the cold state, there arise a variety of problems such as a decline of start-up property, an increase in quantity of fuel consumption, deterioration of an emission of exhaust gas or a decline of performance of the car room interior heating system.
To overcome the variety of problems given above, there have hitherto been proposed a heat accumulation system of an engine as disclosed in Japanese Patent Application Laying-open Publication No. 6-185359 and a heating system for a vehicle as disclosed in Japanese Patent Application Laying-Open Publication No. 10-309933.
The heat accumulation system of the engine disclosed in Japanese Patent Application Laying-Open Publication No. 6-185359, has a heat accumulator provided in a second cooling water passageway in a water cooled internal combustion engine including a first cooling water passageway extending via a cylinder block and the second cooling water passageway extending via a cylinder head.
This heat accumulation system of the engine is constructed to warm up preferentially the cylinder head by circulating the cooling water heated by the heat accumulator through the second cooling water passageway, thereby attempting to warm up an intake system and a fuel supply system.
On the other hand, the heating system for the vehicle disclosed in Japanese Patent Application Laying-open Publication No. 10-309933, includes a water passageway for flowing the cooling water via the internal combustion engine and a heater core, a heat accumulation tank, provided more upstream in a cooling water flowing direction than the heater core, for reserving the cooping water in a way that keeps the heat, an exothermic body, provided more upstream in the cooling water flowing direction than the heat accumulation tank on the water passageway, for heating the cooling water flowing through the water passageway, and an electrically-driven pump, disposed more upstream in the cooling water flowing direction than the exothermic body on the water passageway, for feeding by pressure the cooling water flowing through the water passageway.
This heating system for the vehicle is constructed such that the high-temperature cooling water heated by the exothermic body is reserved in a heat accumulation tank and supplied to the heater core when the temperature of the cooling water is low as at a cold time, thereby enhancing a heating performance.
By the way, in the heat accumulation system of the engine disclosed in Japanese Patent Application Laying-Open Publication No. 6-185359, even after the high-temperature cooling water within the heat accumulator (which will hereinafter be called heat accumulation hot water) has reached the cylinder head, the cooling water continues to circulate, and hence the following problems (1)˜(3) might arise.
(1) The heat accumulation hot water having arrived at the cylinder head from the heat accumulator is discharged from the cylinder head, and the low-temperature cooling water staying previously in the cylinder head again flows into the cylinder head. Therefore, the cylinder head heated by the heat accumulation hot water is cooled by the low-temperature cooling water.
(2) When the heat accumulation hot water flows somewhere other than the cylinder head, the heat of the heat accumulation hot water is transferred to a member excluding the cylinder head.
(3) If the heat accumulation hot water is circulated by an electrically-driven water pump, the electric power consumed by the electrically-driven water pump unnecessarily increases.
Further, in the heating system for the vehicle disclosed in Japanese Patent Application Laying-Open Publication No. 10-309933, the internal combustion engine, the electrically-driven pump, the electric heater, the heat accumulation tank and the heater core are disposed in series sequentially from an upstream side of the cooling water flowing direction. Therefore, the following problems (a)˜(c) might be caused.
(a) If there arises a necessity of supplying the heater core with the cooling water heated by the electric heater, a large quantity of cooling water in the circulation circuit extending via all of the internal combustion engine, the electrically-driven pump, the electric heater, the heat accumulation tank and the heater core, must be heated, resulting in an increase in consumption of the electric power and a decline of the heating performance. Especially because of a large thermal capacity of the internal combustion engine, the heat of the cooling water heated is absorbed by the internal combustion engine.
(b) In the case of supplying the internal combustion engine with the heat accumulation hot water in the heat accumulation tank, the cooling water having flowed out of the heat accumulation tank flows into the internal combustion engine after via the heater core, so that a flow resistance of the cooling water rises. In this case, a quantity of the heat accumulation hot water flowing into the internal combustion engine per unit time decreases, and a quantity of the heat transferred to the internal combustion engine from the heat accumulation hot water per unit time, also decreases corresponding thereto. Hence, the internal combustion engine is not sufficiently preheated, or it takes much time to preheat the internal combustion engine.
(c) When supplying the heater core with the high-temperature cooling water flowing out of the internal combustion engine, the cooling water having flowed from the internal combustion engine flows into the heater core after via the electrically-driven pump, the electric heater and the heat accumulation tank, whereby the flow resistance of the cooling water rises. In this case, a flow quantity of the cooling water flowing into the heater core per unit time decreases, and a quantity of the heat transferred to the air for heating from the cooling water per unit time in the heater core, also decreases corresponding thereto, with the result that the heating performance decreases.
Note that it can be considered for overcoming the problems (b) and (c) given above to individually provide a water passageway bypassing the heater core, a water passageway bypassing the electrically-driven pump and a water passageway bypassing the heat accumulation tank. A problem is, however, that the cooling water circulation circuit becomes complicated, and this leads to a poor mountability of the vehicle heating system into the vehicle.